4/14/2010

KEITH CONNOLLY

TATJANA TREBIC

OPTIMIZATION OF A BACKYARD AQUAPONIC FOOD PRODUCTION SYSTEM

BREE 495 Design 3 Bioresource Engineering Presented to Dr. Vijaya Raghavan

Faculty of Agricultural and Environmental Sciences Macdonald Campus, McGill University

Acknowledgements

We extend our warmest thanks to the following people for their inspiration, guidance and support:Mr. Damian HInkson, Chairman (Bairds Village Aquaponic Association) Susan Mahon, Internship Coordinator (Barbados Field Study Semester) Inter-American Institute for the Cooperation on Agriculture (Barbados Branch) Dr. Inteaz Alli, Director (Barbados Field Study Semester) Dr. James Rakocy (University of the Virgin Islands Agricultural Experiment Station) Dr. Suzelle Barrington, Dr. Vijaya Raghavan and the Bioresource Engineering Department (McGill University)

Table of ContentsAcknowledgements....................................................................................................................................... 2 Executive Summary....................................................................................................................................... 6 1. Introduction .......................................................................................................................................... 8 1.1 Food Security ...................................................................................................................................... 8 1.2 Small-Scale Agriculture ....................................................................................................................... 9 1.3 Objective of Project .......................................................................................................................... 10 2. Background ......................................................................................................................................... 11 2.1 Agriculture in Barbados .................................................................................................................... 11 2.1.1 Economy and Human Resources ............................................................................................... 11 2.1.2 Natural Resources ...................................................................................................................... 11 2.1.3 Climate ....................................................................................................................................... 12 2.1.4 Terrain ........................................................................................................................................ 13 2.1.5 Crop Production in Barbados ..................................................................................................... 13 2.2 Food Production Methods ................................................................................................................ 14 2.2.1 Aquaculture................................................................................................................................ 14 2.2.2 Hydroponics ............................................................................................................................... 15 2.2.3 Aquaponics................................................................................................................................. 16 2.2.4 Comparison of Food Production Methods................................................................................. 19 3. Aquaponic Systems ............................................................................................................................. 21 3.1 System Designs ................................................................................................................................. 21 3.1.1 Media Filled Systems ................................................................................................................. 21 3.1.2 Flood and Drain .......................................................................................................................... 21 3.1.3 Nutrient Film Technique (NFT)................................................................................................... 22 3.1.4 Floating Raft System .................................................................................................................. 23 3.2 Fish .................................................................................................................................................... 24 3.2.1 Fish Selection ............................................................................................................................. 24 3.2.2 Culturing Conditions for Tilapia ................................................................................................. 25 3.2.2.1 Water Quality .......................................................................................................................... 25 3.2.2.2 Feed......................................................................................................................................... 28 3.3 Plant Crops ........................................................................................................................................ 29 3.3.1 Nutritional Requirements .......................................................................................................... 29

3.3.2 Crop Selection ............................................................................................................................ 30 3.4 Bacteria ............................................................................................................................................. 31 4. The Design........................................................................................................................................... 33 4.1 System Stocking Density ................................................................................................................... 34 4.1.1 Growing Area ............................................................................................................................. 34 4.1.2 Basil, Okra and Coconut Husk .................................................................................................... 34 4.1.3 Component Ratios ......................................................................................................................... 36 4.1.4 Feed Rate Ratio and Annual Fish Feed Mass. ............................................................................ 36 4.1.5 Feed Conversion Ratio ............................................................................................................... 37 4.1.6 Fish Biomass Production ............................................................................................................ 37 4.1.7 Fish Stocking and Harvest .......................................................................................................... 37 4.1.8 Plant Stocking and Harvest ........................................................................................................ 39 4.2 Water Flow Rate ............................................................................................................................... 40 4.2.1 Hydraulic Loading Rate .............................................................................................................. 41 4.2.2 Hydraulic Retention Time .......................................................................................................... 42 4.3 System Components ......................................................................................................................... 42 4.3.1 System Configuration ................................................................................................................. 42 4.3.2 Fish Tank .................................................................................................................................... 46 4.3.3 Grow Bed.................................................................................................................................... 48 4.3.4 Sump Tank.................................................................................................................................. 49 4.3.5 Aeration System ......................................................................................................................... 49 5. Other Considerations .......................................................................................................................... 55 5.1 Temperature Regulation ................................................................................................................... 55 5.2 pH Regulation.................................................................................................................................... 56 5.3 Water Quality Testing and Debris Control ........................................................................................ 56 6. Cost Benefit Analysis ............................................................................................................................... 57 6.1 Costs .................................................................................................................................................. 57 6.1.1 Initial Material Costs .................................................................................................................. 57 6.1.2 Annual Costs............................................................................................................................... 58 6.2 Outputs ............................................................................................................................................. 59 6.2.1 Fish Production .......................................................................................................................... 59 6.2.2 Vegetable Production ................................................................................................................ 59

6.3 Summary of Analysis ......................................................................................................................... 60 7. Conclusions ......................................................................................................................................... 61

Bibliography ................................................................................................................................................ 62 Appendices.................................................................................................................................................. 67 Appendix A: Barbados Background Information .................................................................................... 67 Appendix B: Water Quality Experiment Results from Barbados System ................................................ 68 Appendix C: Fish Growth Estimations ..................................................................................................... 71 Appendix D: Air Pump Specifications ...................................................................................................... 73

Executive SummaryThe current and escalating extent of soil degradation, water scarcity and climate-related challenges plaguing agricultural productivity in every corner of the world and particularly in the most underdeveloped and resource-scarce regions demands for a re-evaluation of the way we produce the foods that keep us alive and seems to beg for what could be referred to as another green revolution. The need for the development of innovative, resource efficient and locally appropriate agricultural solutions is immense and this need is greatest in densely populated, resource-poor nations with small economies. Tropical island nations face increasing confrontations by climate change and obstacles to the sound stewardship of their natural resources and environment and trends in land use allocation indicate the deteriorating status of agricultural activities as lucrative compared to industries such as tourism, real estate and off-shore financing. The end results are the massive rates of food importations from distant locations, the decline of regional agricultural autonomy and a loss of connection between consumers and the origin, nutritional value and safety of their food. The small eastern Caribbean nation of Barbados faces many of these challenges, yet with a highly educated workforce and a climate conducive to year-round food production, it has the potential to transform its agricultural industry by employing new food production technologies that can be applied to the local context while placing minimal stress on the countrys already scarce water and agriculturally-productive soil resources. Aquaponics is a concept relatively new to modern food production methods and provides answers to many of the above-mentioned problems. The technology combines the two well-established practices of aquaculture and hydroponics to yield a method of food growing that greatly reduces the use of water resources, demands no soil at all, and produces high yields of fresh, nutritious crops in the form of vegetables, fruits, herbs and fish. Aquaponics on a small scale can serve as a familys solution to the need for an inexpensive, nutritious and reliable food source that has the capacity to provide a full meal (vegetables and protein) without many inputs. The optimization of one such small-scale, backyard aquaponic food production system is the subject of this report whereby an improved design is delivered in response to practical experience gained during an internship with the Bairds Village Aquaponic Association in Barbados over the Fall of 2009.

This report details the improvements in the configuration and overall health of the backyard aquaponic systems seen in Barbados through the inclusion of an effective aeration system, a method of water-level regulation, a different and more efficient system of water pumping/distribution, as well as measures for the assurance of high system water quality and increased crop yields. The importance and

appropriateness of aquaponics as a solution in Barbados is explored along with the key parameters required for a high-performance aquaponic food production system.

1. Introduction1.1 Food SecurityPopulations around the world face questions of food security today on a scale that has not been seen in recent human history. The evolution of how we feed our populations and the technologies we use to do it have created a unique set of circumstances that bring with them unique challenges, and despite significant advances in food production and our knowledge of food nutrition and food safety, hunger continues to plague millions of people around the world. It is thought that over a billion people in the world are currently undernourished (World Food Programme, 2010). Many factors contribute to

hunger and decreasing food security in the world today including conflict, poverty, poor agricultural infrastructure and over-exploitation of the environment. The concept of food security is defined by the Food and Agriculture Organization of the United Nations (FAO) in the following way: Food security exists when all people, at all times, have physical, social and economic access to sufficient, safe and nutritious food which meets their dietary needs and food preferences for an active and healthy life. Household food security is the application of this concept to the family level, with individuals within households as the focus of concern. Key among the issues that threaten food security are the intensive resources needed for agricultural activities. Agriculture is by far the largest strain on the worlds precious freshwater resources, currently accounting for 70% of the worlds freshwater consumption (Pimentel, Berger, Filberto, & Newton, 2004). Some predictions have human consumption of the worlds freshwater resources at over 90% by 2025 (2003 International Year of Freshwater, 2003). Increasing water scarcity has given rise to an unprecedented water conservation movement, although consumption levels remain at all time highs. Agricultures dependence on healthy soil presents another problem in food production, as current estimates are that 38% of global agricultural land is degraded. Soil degradation is the change induced by the natural decrease in the soils potential for productive use, and normally results in reduced yields due to lack of or insufficient nutrients or water availability. Improper land use and poor land

management have been singled out as the most important factors leading to soil degradation (The World Bank, 2010). To add value to the soils nutrient stock, agricultural trends have been to add

increasing amounts of fertilizer, which, along with herbicides and pesticides, has contributed to significant and disquieting environmental problems. Access to food is another obstacle that families and countries face when considering food security. Often it is difficult or unfeasible to grow food locally and a global trend for many has been to obtain food that has been grown far from the point of purchase. However, many developing countries lack the infrastructure such as roads or storage facilities to make this scenario effective and sustainable. In

addition, this situation makes millions of people vulnerable to market related supply problems associated with distant producers.

1.2 Small-Scale AgricultureModern agriculture has slowly evolved to fit a capitalist, industrial model where farming is done on large scales by relatively few farmers. Multi-national corporations now control such a large portion of the food production process that the people they feed have become increasingly dependent and vulnerable to their abilities and philosophies. Industrialization of any process theoretically is the most efficient use of our resources, however the allocation of our food production to a few powerful institutions has resulted in the development of significant food security and environmental problems. Decreasing genetic diversity in our food production, genetically altered food, and the large energy requirements to package, preserve, and transport food are just some of the issues brought on by the industrialization of our food system. Given the problems associated with intensive farm practices, and given the global scarcity in soil and water resources along with the problems associated with under-developed regions where hunger prevails, there has been a large push toward more sustainable farming practices in an effort to feed more people with increasing efficiency while reducing our impact on the environment. farming is an alternative to intensive farming. resources. Urban agriculture is defined as the practice of cultivating, processing, and distributing food, in or around (peri-urban), a village, town or city (Bailkey & Nasr, 2000). It is being recognized as one of the activities that has the potential to contribute toward socio-economic development in urban areas of the developing world and has the capacity to contribute to alleviating food insecurity and poverty. Studies show that urban agriculture contributes significantly to household income and gives families access to inexpensive food, consequently reducing poverty (Hampwaye, Nel, & Ingombe, 2009). Small scale

It acknowledges agricultures dependence on finite

Such an agricultural method is the subject of the design project that follows.

Aquaponics is the

combination of hydroponic and aquaculture systems, whereby fish tank water that has become nutrient rich by the excretion of fish is circulated into a growing area where the nutrients are absorbed by plants that are cultured hydroponically. At the same time the grow bed acts as a biofilter and cleans the water so it can be recirculated back to the fish tank. The closed system uses a fraction of the water, no soil, and produces two food sources for consumption; the crops grown in the bed, and the fish reared in the tank. Aquaponics is garnering growing attention around the world because of its efficient use of

resources. It provides a simple and practical solution to the food security issues previously discussed and has the potential to increase the health and stability of families by feeding them and helping them become financially secure.

1.3 Objective of ProjectIn the Fall of 2009, Keith Connolly and Tatjana Trebic, the authors of this project, took part in the Barbados Field Study Semester where they were partnered with the Bairds Village Aquaponic Association (BVAA), which had just received a United Nations Development Fund grant to develop a community sized aquaponics operation in the community of Bairds Village. During the internship, Keith and Tatjana did promotional work with the organization and helped in the construction of several systems, including one that they housed at McGill Universitys Bellairs Research Institute on which they conducted water quality tests. Tilapia were used in all these systems and in the McGill system okra and basil were grown. Mr. Hinkson, the founder of the Bairds Village Aquaponic Association, had been working with aquaponics for several years, but didnt have a very scientific approach to minimizing his inputs and maximizing his outputs. Thus was born the objective of this project: To design an improved aquaponics system and make management recommendations with the goal of optimizing fish and plant biomass outputs.

2. Background2.1 Agriculture in Barbados2.1.1 Economy and Human Resources The easternmost Caribbean island nation of Barbados (see Figure 39 in Appendix A) is considered to be the most developed of the Caribbean states, having one of the highest per capita incomes in the region. Its political stability, relative proximity to North American markets and exceptional natural beauty/biodiversity make it a desirable market for foreign investment. Foreign exchange includes offshore financing and information services as well as significant trading with the United States, Canada and other Caribbean states, with services making up 80% of national exports. Tourism and the light industry make up 75% of the national GDP while agriculture contributes a mere 6% (Central Intelligence Agency, 2010). Barbados has economic strengths in that it shares the same time zone as the eastern United States and Canadian financial centers, has English as its official language, making communications with Canada, the United States and the United Kingdom seamless, and a has a highly educated workforce with a literacy rate of 99.7% (Central Intelligence Agency, 2010). The small size of Barbados and other nations in the region does not allow for economies of scale, however, regional cooperation through entities such as The Caribbean Community (CARICOM) allows for the free movement of labour and capital, the coordination of agricultural, industrial and foreign policies as well as access to a Common Market. Such collaboration among Caribbean states strives to improve standards of living in its member countries, enhance international competitiveness and increase productivity among other goals for the development and prosperity of the region (CARICOM, 2009). 2.1.2 Natural Resources The densely populated island nation of Barbados (627 people/km2) has limited resources required for a prosperous agricultural industry (Central Intelligence Agency, 2010). This high population density and seasonal influx of foreign tourists - over 570,000 tourists stayed in Barbados in 2007 and over 600,000 cruise ship passengers visited the country that same year places stress on the countrys key national resources (Totally Barbados, 2010). Barbados is known as the 15th most water scarce country in the world and freshwater withdrawal per capita is 333 m3/year (Central Intelligence Agency, 2010). Internal Renewable Water Resources are on

the scale of 0.082 km3/year, groundwater from infiltrated rainfall supplies 0.074 km3/year, while surface waters make up 5.8 million m3/year (FAO, 2000). Average daily water use by the agricultural sector amounts to approximately 10.4 ML/day (or 10, 400 m3/day) and an estimated 1026 ha are irrigated by potable water (UN, 2004). This makes up 5.9% of the countrys total cropland (EarthTrends, 2003). Total renewable water resources amount to 0.1 km3 (Central Intelligence Agency, 2010). The land surface of the island is composed mostly (~83%) of coralline limestone, while the remaining 17% is made up of shales, sands and clays (FAO, 2000). The limestone that covers most of the nation is highly porous and allows for very rapid infiltration of rainwater, meaning that its capacity to retain water in the root zone is quite low ( Ministry of Agriculture and Rural Development). The northeastern region of the island, called the Scotland District is made up of layers of shales, sands and clays. It is quite rugged and is characterized by high overland runoff, frequent landslides and surface soil erosion problems (FAO, 2000). The long history of intensive plantation-style monoculture production over the past 300 years in Barbados has made extensive contributions to soil quality problems in Barbados. These include the erosion of topsoil, a decrease in soil fertility, and the consequent application of large amounts of fertilizer and pesticides in order to maintain productivity (Homer, 1998). 2.1.3 Climate Barbados has a tropical oceanic climate with little variation in temperatures due to the cooling easterly trade winds from the Atlantic Ocean. The rainy season lasts from June to December, but the island is considered to be relatively arid in comparison to other Caribbean nations. (FAO, 2000) The country is part of the hurricane belt, however, the frequency of hurricanes hitting Barbados is extremely low. Average temperatures during the day reach about 27 oC (see Figure 40 in Appendix A for data on temperature, wind speed, humidity, rainfall, and other weather parameters typical to Barbados) and range approximately from 20 to 32oC. In a typical year, an average rainfall of 760 mm along the coastal areas to 2000 mm in thecentral parts of the island are common (Economic and Social Development Department (FAO), 2005),

but rainfall amounts may be lower than 25 mm per month during the dry season (FAO, 2000).

On average throughout the year, Barbados receives 8 to 9 hours of sunshine each day (see Figure 40 in Appendix A). 2.1.4 Terrain The island of Barbados is mostly flat with a gentle upwards slope from the coast towards the inland (Central Intelligence Agency, 2010). The predominant coralline limestone regions are divided into three terraces rising towards the interior of the island with a peak elevation of 343 m above sea level (AXSES Systems Caribbean Inc.), and are lined with deep gullies running from high elevations at the Scotland District to the coast (FAO, 2000). 2.1.5 Crop Production in Barbados The colonial history of Barbados has left behind a reliance on monocrop, plantation-style agriculture which focuses on the production of a single cash crop in large amounts. The agricultural industry in Barbados therefore still consists primarily of sugar cane cultivation and the sugar, rum and molasses production industry. In the 2007/2008 growing season, 31.7 thousand tonnes of cane were harvested on 5.9 thousand hectares of land (IICA, 2009). Sugar, a cash crop, most of which is exported, is however on the decline and its future as a significant sector of the countrys economy is in peril due to poor quality soils, high cultivation costs, sporadic droughts and low global sugar prices (FAO, 2008). The proportion of land in the country that is arable is 37% (about 22, 472 ha), while only 2.3% of the land is used to grow permanent crops (FAO, 1999). Other crops include cotton, root crops, corn, onions, other vegetables, bananas, plantains, figs, other fruits, cut-flowers and foliage (Homer, 1998). Production of food crops in the country is quite low as Barbados imports around 80% of its food (IICA, 2009), including large amounts of fruits and vegetables (Zvodsk & Dolly, 2009). Only 10% of the labour force in Barbados is involved in agricultural activities as agriculture must compete with more profitable industries and forms of land use such as the growing tourism and real-estate sector (CIA World Factbook, 2009). The reliance on outside factors and world markets associated with such high levels of food importation place the country in a position of dependency and hinders progress towards self-sufficiency in terms of food production. Barbados agricultural trade deficit in 2004 was US $67.5 million (FAO, 2008).

Future plans for the promotion of small-scale farming by the Ministry of Agriculture and Rural Development will encourage local production of food crops and small livestock, which will give Barbadians increased food security and greater independence in the generation of their household incomes (Zvodsk & Dolly, 2009). Traditionally, small-scale farming faces challenges regarding the necessity to incorporate high-input technologies into their production in order to be able to compete on the global market. These technologies involve high costs and significant initial investments that cannot be afforded by all rural food producers and which increase production costs and therefore the cost of locally produced crops. This makes small farmers uncompetitive against cheaper imported items (Zvodsk & Dolly, 2009). There is a great local need for innovative agricultural solutions that can be applied to the Barbadian context and which ensure the feasible, small scale production of food by average Barbadian families. An appropriate and accepted solution will therefore contribute to decreased dependency on foreign imports which involve transportation across great distances and are generally highly unsustainable. Aquaponics has the potential to lessen the challenges associated with small scale farming in Barbados and generally in the Caribbean. The system requires minimal land and water resources, and no soil resources, which is desirable for highly populated and arid regions such as Barbados. Aquaponic systems provide a source of protein as well as fresh fruits, vegetables or herbs. As meat on the island is relatively expensive, protein in the form of freshwater fish would provide a healthy alternative and reduce stress on dwindling saltwater and freshwater fish supplies.

2.2 Food Production Methods2.2.1 Aquaculture Aquaculture is the cultivation and rearing of aquatic plants and animals in a fully or semi-controlled environment. Many species are produced around the world by means of aquaculture including both freshwater and saltwater fish, crustaceans, and molluscs, along with plants such as seaweed. The

origins of aquaculture date back thousands of years. There are different theories as to how the practice came about but it is generally thought to have developed independently in several parts of the world, usually by a low-lying area of land being flooded and stocked with fish during high tide or rainy season and the surrounding human population implementing preliminary aquacultural practices to maintain the fish in order to have a reliable food source (Herminio, 1988).

Freshwater finfish, particularly Chinese and Indian carp species, account for the greatest share of total aquaculture production, followed by molluscs. Although low in production quantity, some of the minor product groups, such as shrimp and marine fish, have a disproportionate economic importance because of their high unit value. The most harvested species in recent years have been the Pacific cupped oyster and the silver carp. By 2006 aquaculture was provided nearly 50 percent -- or 51.7 million tonnes -- of all world fisheries production (Aquaculture resources, 2010). The latter half of the 19th century saw the capacity of commercial fishing increase at unprecedented rates. The result was the plummeting of fish stocks around the world forcing some fisheries, such as the North Atlantic cod fishery, to be completely shut down to recover. The state of the worlds oceans is in dire circumstances, whereas demand and consumption for seafood is at an all time high. Aquaculture will be a powerful tool to reconcile this paradox. Current predictions are that aquaculture production will need to reach 80 million tonnes by 2050 to keep pace with seafood consumption. (Aquaculture resources, 2010). Many different forms of aquaculture take place at varying levels of intensity and scale. In mariculture, organisms are usually cultured in sheltered marine environments, whereas integrated multi-trophic aquaculture combines multiple organisms in a tank attempting to use the waste from one, such as fish, for the input of another, such as seaweed. Many significant issues are present within the world of aquaculture. Decreasing genetic variation

associated with fish farming, competition between wild and farmed animals, propagation of diseases associated with aquacultures high stocking densities, and waste management are but to name a few. In-shore aquaculture requires massive amounts of water exchange to keep water quality at non-toxic levels. Finding uses for the wastewater produced in aquaculture has proved to be a laborious and

cumbersome endeavour. 2.2.2 Hydroponics The word hydroponics is taken from the Greek words hydro, meaning water, and ponos, meaning labour. It is a method of growing plants using a mineral nutrient solution in water, without soil. In traditional agricultural methods soil is used as the medium whereby nutrients are dissolved in water, which can then be taken up by the plant roots, although the soil itself is not necessary. If nutrients are added to the water in which the plants are grown, then the soil medium is not needed. Although the technique is thought to be a technologically advanced manner to grow plants, hydroponic methods, or

at least ones with their roots in hydroponics, have been used for centuries and are quite simple to employ. The hanging gardens of Babylon, the floating gardens of the Aztecs of Mexico and those of the Chinese are all precursors to modern day hydroponic cultures. For the purposes of this paper the term hydroponics is applied to systems using growing media, in our case coconut husk, as will be discussed later. Systems using some form of growing media that is not soil are designated as simply soilless culture. Both soilless culture methods and hydroponics methods use a nutrient solution but hydroponics is generally thought of as a subset of soilless culture since it does not employ media to support the root structure of the plants. The ability to grow plants in areas where soil is not conducive for in-ground agriculture is the great advantage of hydroponics. Also, it is much more efficient in its water use as water stays in the system and can be reused, as opposed to it percolating through the soil and ultimately replenishing the groundwater reserves. Having greater control over nutrient levels results in healthier crops, fertilizers which often contribute to pollution are not used, pesticides are not needed to deal with pests, and ultimately, much higher and more stable crop yields are achieved. Hydroponic methods have been the subject of much research during the last century as more focus has been put on our agricultural methods. As a result, many advances have been made in the field and

current hydroponic methods take many forms. The types of systems possible will be further discussed while outlining the hydroponic component of aquaponics systems, however as noted above, whether the system uses a media or not is a primary distinction. If there is no media employed in an aquaponic system, the plant roots are exposed to the nutrient solution directly. Among these types of systems are the nutrient film technique (NFT), flood and drain technique, deep water culture technique and raft technique. 2.2.3 Aquaponics Aquaponic systems combine the two forms of agricultural production mentioned above, recirculating aquaculture and hydroponics. Aquaponics provides a solution to the main issues these two systems face; the need for sustainable ways of filtering or disposing of nutrient-rich fish waste in aquaculture and the need for nutrient-rich water to act as a fertilizer with all of the nutrients and minerals needed for plants grown through hydroponics (Nelson, 2008). Combining these two systems provides an allnatural nutrient solution for plant growth while eliminating a waste product which is often disposed of as wastewater.

In these systems, the fish grown in a freshwater tank secrete wastes through urine and through their gills into their surrounding tank water. Over time, these waste compounds, which are toxic to the fish accumulate and compromise fish health, but can be used as an organic fertilizer for plants (Nelson, 2008). This nutrient-rich effluent is used to irrigate a connected hydroponic bed while fertilizing its plant crops at the same time. The nutrients, largely in the form of ammonia are converted by denitrifying bacteria in the hydroponic grow bed into forms readily uptaken by plants for energy and growth. Essentially, the hydroponic bed and its crops serve as a biofilter for the fish waste water before it is returned, cleaned back into the fish tank. Thus, the waste of one biological system becomes nutrients for another biological system (Diver, 2006). See Figure 1 for a conceptual diagram of the nutrient/water flows in a general aquaponic system.

Nutrient-rich fish waste effluent

Clean, filtered water

Figure 1: Conceptual diagram of nutrient recycling in aquaponic systems (Adapted from (Suits, 2010))

Aquaponics allows for the growth of a full meal (protein from fish and fibre, nutrients and minerals from vegetable, fruit, or herb production) in one closed-loop system, where the cultivation of two types of crops (fish and plants) is accomplished using only one body of water and one infrastructure. Crops are grown in a concentrated manner without compromising the health of the system and while greatly reducing the required input of water resources (Nelson, 2008) and increasing the value gained from the continuously cleaned and recycled water (Considine, 2007).

Aquaponics is an extremely resource-efficient and sustainable method of producing crops on any scale (Suits, 2010) that imitates the plant-fish interactions found in a natural waterway. See Figures 2 and 3 for various sizes of aquaponic systems.

Figure 2: A small system, built using recycled barrels (Hughey, 2005).

Figure 3: A commercial-sized raft aquaponics system (Rakocy, Masser, & Losordo, 2006)

When the system is in balance, high production of fish and plant crops at high stocking densities can be obtained without the use of chemical fertilizers, herbicides or pesticides (Nelson, 2008). A small aquaponic system in the backyard of a Barbadian family could go a long way in providing exceptionally fresh food daily and promoting local food production as well as supporting the local economy (Diver, 2006). This type of backyard agriculture allows for the production of various plant crops in a small space that can be used in the home kitchen or can be sold on the local market. Aquaponic systems can provide food year-round (even during the dry season) in arid regions where water and soil resources may be scarce and can act as the key to self-sustenance for communities living in developing regions of the world and normally depending on world food markets (Hughey, 2005). The lack of a need for soil in these systems implies that they can be used in urban regions and in places with poor soil quality (Nelson, 2008). In order to feed the worlds growing population, there will be a great need for highly productive, urban and sustainable food production systems (Nelson, 2008). Increasing health consciousness and world demands for fish supplies require a solution such as aquaponics which integrates two separate systems which individually can meet these needs partially, but combined can provide an answer to the greater

picture with increased resource-efficiency and at a lower cost (Diver, S., 2000), all while giving individuals and families greater control over the quality, safety and origin of their food. 2.2.4 Comparison of Food Production Methods Aquaponic food production is very versatile in that it can be used on a commercial scale or at the level of home food production. It combines many of the advantages of other methods of food production (such as aquaculture and hydroponics) with additional advantages unique to aquaponics. In comparison to hydroponics, aquaponics also does not require soil for the abundant, year-round growth of food and provides the elements minerals and nutrients as well as the structural support that traditionally is provided by soil. Both systems also allow for high crop densities and the conservation of water. No water is lost in these systems to soil outside of the root zones or to weeds which populate soil systems. Additionally, the risk of soil-borne disease is not present (Nelson, 2008). The large amounts of time and resources that hydroponic growers spend mixing the perfect fertilizer solution from manufactured or mined compounds in order to meet all of the nutritional requirements of the plants are reduced simply and significantly in aquaponics (Nelson, 2008). Aquaponics does not require the addition of synthetic, chemical fertilizer as the fish waste from the rearing tank provides adequate amounts of the essential ammonia, nitrate, nitrite, phosphorus, potassium and micronutrients as well as some secondary nutrients for the healthy growth of hydroponic plants (Diver, 2006). The use of synthetic herbicides and pesticides is also unnecessary and would greatly compromise the health of the fish who are highly sensitive to water quality. Aquaponics is therefore essentially an organic form of hydroponics (Nelson, 2008) whose only fertility input is fish feed containing about 32% protein. Aquaponics also provides an entirely separate crop in addition to plant crops the fish (Spade, 2009). In comparison to aquaculture, an aquaponic system can house fish at a high stocking density provided that the water is regularly filtered and aeration is regularly performed along with the monitoring of all water quality parameters relevant to the health of the fish. Both systems can be housed nearly anywhere due to the small amount of space they require and can therefore provide fresh fish to a community on a regular basis. Recirculating aquaculture, however has been criticized for its high rate of failure as the high stocking of fish leaves little room for error in terms of water quality and therefore of fish health. Water in these systems must be mechanically or biologically filtered with extreme care and all parameters must be

carefully maintained. A large waste stream of fish waste is also produced in aquaculture and it needs to be disposed of somehow. Additional water inputs are needed to ensure water quality. An aquaponic system provides solids removal and biofiltration of the fish waste effluent as well as additional cleaning by the assimilation of nutrients into plant biomass. The waste stream from aquaculture is eliminated and an additional type of crop (plants) is obtained (Nelson, 2008). In terms of resource efficiency, aquaponic systems use 1% of the water required in pond aquaculture to raise the same yield of tilapia fish a species commonly used in recirculating aquaponic systems (Diver, 2006).

Aquaponics combines the advantages of both hydroponics and aquaculture, while eliminating the disadvantages of both systems. It also reduces operating costs in comparison to either of these methods alone. A comparison of the above mentioned systems along with comparison to organic farming is summarized in Table 1 below.Table 1: Comparison of various forms of food production (adapted from Comparison of Methods table in Nelson, 2008).

Advantages Organic Farming Inorganic Hydroponics Presumed as a healthier method of growing food than commercial farming and thus has become popularized. Uses organic wastes as fertilizer. Uses natural pest control. Tends to produce better tasting and at times more nutritional crops. High volumes of food are produced in a small space. Has potential for year-round production if controlled. High biomass of fish produced in a small space. All of the advantages of the other methods and additionally: Reuse of fish waste as nutrients for plants. Fish dont carry the pathogens (e.g. E.coli and Salmonella) found in warm-blooded animals. Imitates a natural cycle and is the most sustainable of the four methods. Consistent fish biomass in the fish tanks lets plant growth thrive. -

Disadvantages Requires more land than conventional farming. Often higher costs to grow and certify crops. Agribusiness is quickly replacing small-scale organic operations. Highly dependent on costly manufactured/mined fertilizers.

-

Recirculating Aquaculture Aquaponics

-

-

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High rate of failure due to small margin for error. Large waste stream produced. Operator must have knowledge of both fish and plant production. Major fluctuations in fish stocks in the tank can disrupt plant growth.

3. Aquaponic Systems3.1 System DesignsThere exist several system designs for recirculating aquaponics systems. The designs are based on hydroponic systems, the difference being that the water source for the aquaponics system come from the fish tank and is eventually returned to its source of origin. 3.1.1 Media Filled Systems The hydroponic component is first distinguished by whether it employs a media or not. This becomes very important in aquaponic systems because the presence of a media that plant roots are grown in can possibly eliminate the need for a separate settling tank and biofilter. Sludge and solid from the fish tank get caught in the media and are processed by bacterial communities that develop in the media, thereby acting as a biofilter and eliminating the need to remove the solids in a separate system. If the system does not employ a media and plant roots are exposed directly to the water, then a settling tank and biofilter are necessary to return the water quality to sufficient levels in which fish can live (Rakocy, Masser, & Losordo, 2006).

Figure 4: Various grow media in media-filled systems (Hydroponics: Andrew Smith, 2006)

3.1.2 Flood and Drain (also known as Ebb and Flow) In flood and drain systems, plant roots are exposed to a static nutrient solution for hours at a time before the solution is drained away, which could happen several times a day. The technique can be used regardless of whether a media is used in the system, and plant roots could either be completely submerged, or partially submerged, leaving a portion exposed to the atmosphere. Flood and drain systems are noted for their simplicity, reliability and user-friendliness.

Figure 5: Different stages of a flood and drain system (Types of Hydroponics Systems: Dave's Hydroponics Experiment, 2010)

3.1.3 Nutrient Film Technique (NFT) Nutrient film technique consists of the plant roots being exposed to a thin layer of nutrient water than runs through most often a PVC pipe. The idea is that the shallow flow of water only reaches the

bottom of the thick layer of roots that develops in the trough while the top of the root mass is exposed to the air, thereby receiving an adequate oxygen supply. Channel slope, length, and flow rate must all be calculated to make sure the plants receive sufficient water, oxygen, and nutrients. If properly

constructed, NFT can sustain very high plant densities. In aquaponic NFT systems, the biofilter becomes crucial as there is no large surface area whereby bacteria communities can develop (Nelson, 2008).

Figure 6: A pipe NFT system (What is Aquaponics: The Fish Farm, 2010)

Figure 7: A trough NFT system (About Hydroponics: Get up and Grow, 2007)

3.1.4 Floating Raft System Another system that has great potential for commercial use is the floating raft system. In this system plants are grown on floating Styrofoam rafts. The rafts have small holes cut in them where plants are placed into net pots. The roots hang free in the water where nutrient uptake occurs. A major difference between the raft systems and the NFT and media based systems is the amount of water used. The water level beneath the rafts is anywhere from 10 to 20 inches deep and as a result the volume of water is approximately four times greater than other systems. This higher volume of water results in lower nutrient concentrations and as a result higher feeding rate ratios are used. Bacteria form on the bottom surface of the rafts but generally, a separate biofilter is needed. Also, the plant roots are exposed to some harmful organisms that reside in the water, which can affect plant growth.

Figure 8: Schematic diagram of the floating raft system (Growing Arrangements: Sara's Aquaponic Adventure, 2008)

Figure 9: A larger floating raft system (Hydroponic Photo Gallery: The Torch Work Shop)

3.2 Fish3.2.1 Fish Selection The type of fish used in an aquaponic system depends on the climate which will surround the aquaponic system and therefore the temperature the grower is able to maintain, the kinds of fish that the local fisheries department has specified as legal (there are sometimes restrictions on the cultivation of fish that are not native to the region), the type of fish desirable for consumption by consumers and the type of fish feed available to the grower (Nelson, 2008). There are a number of freshwater fish both warm-water and cold-water species that can be adapted for cultivation in recirculating aquaculture systems. These include tilapia, trout, perch, Arctic char (Diver, 2006), blue gill, largemouth bass, channel catfish, koi carp, goldfish, barramundi, murray cod, jade perch (Nelson, 2008), crappies, rainbow trout, pacu, common carp and Asian sea bass (Rakocy, Masser, & Losordo, 2006). Others beyond this list include warm-water fish that are hardy and can adapt to commercial fish feed and high levels of crowding (Nelson, 2008), including some ornamental fish (Rakocy, Masser, & Losordo, 2006). The hybrid striped bass is one species that reportedly does not perform well in aquaponic systems as it cannot tolerate high potassium levels a common supplement used for plant growth (Rakocy, Masser, & Losordo, 2006).

Most commercial systems, however, culture tilapia. Tilapia is a tropical fish originating from the Near East and Africa (Nelson, 2008) that can be well adapted to recirculating tank aquaculture and is exceptionally resilient against fluctuations in dissolved oxygen levels, temperature, pH and dissolved solids (Diver, 2006). Figure 10 below shows a typical tilapia species used in aquaculture.

Figure 10: Red Tilapia fish at harvest (My Mom-Friday, 2009)

The temperature range that tilapia enjoy also correlates to ideal temperatures for the growth of aquaponic plants. Tilapia are the fastest growing of the species used in aquaponic systems (Nelson, 2008) and due to their resilience, their use and therefore the literature available on their cultural procedures is much more developed and thorough (Diver, 2006). The white-fleshed meat of tilapia is popular due to its desirable culinary properties of taste and texture. Virtually unknown in the US in the 1990s, tilapia is now the 6th most consumed seafood product in the country and its popularity continues to grow (Nelson, 2008).

A member of the cichlid family, tilapia is the most widely cultured fish in tropical and subtropical areas of the world and has also been introduced to Japan, India and throughout Asia, Russia, Europe and also the Americas (Nelson, 2008). 3.2.2 Culturing Conditions for Tilapia Although very dependable and resilient to changing conditions, tilapia like all other fish species have certain conditions at which they grow best. 3.2.2.1 Water Quality Good water quality must be maintained at all times in a recirculating fish tank to maintain optimal growth conditions and health of the fish. Regular water quality testing is essential and can be

performed using water quality testing kits obtained from aquacultural supply companies. The most critical water quality parameters to monitor are dissolved oxygen concentrations, temperature, pH, and nitrogen from ammonia, nitrate and nitrite. Nitrogen in the form of nitrate and nitrite usually does not present a water quality problem in aquaponic fish tanks as nitrite is quite quickly converted to nitrate and nitrate itself is only seriously toxic to fish at very high levels (300-400 mg/L). The biofiltration mechanism in aquaponic systems also removes nitrates quite well and can keep their concentration at much lower levels than this (DeLong, Losordo, & Rakocy, 2009). Thus the most important water quality parameters to design and make practice recommendations for are temperature, dissolved oxygen and ammonia. Other important parameters include salinity, phosphate, chlorine and carbon dioxide. Other factors that influence the quality of fish tank water include the stocking density of the fish, their growth rate, the rate at which they are fed, the volume of water in the system and environmental conditions (Diver, 2006). The ideal values for tilapia water quality parameter requirements critical for the design of aquaponic systems (which are explained below) are summarized in Table 2.

Table 2: Summary of ideal water quality conditions for an aquaponic fish tank

Parameter

Optimal Range for Fish Tank in Aquaponic Systems 6.0-7.0 mg/L 22.2-23.3 C 6.5 - 7